基于CLM模式的青藏高原土壤冻融过程陆面特征研究

Land surface characteristics in soil freezing and thawing process on the Tibetan Plateau based on Community Land Model

使用位于青藏高原东部若尔盖站的观测数据驱动CLM3.5模式,设计一组去除模式中冻融过程的"退化试验",进行为期一年的模拟研究。通过对比原试验与敏感性试验模拟结果,初步分析冻融过程在土壤温度变化、各能量通量分配中的作用,得到以下结论:(1)冻融过程是土壤温度变化的"缓冲器",冻结过程向周围环境释放能量减缓了土壤降温的速率,使土壤温度不至降得太低,而消融过程从周围环境吸收能量减缓了土壤升温的速率,使土壤温度不至升高太多;(2)冻融过程改变了地表辐射通量,土壤冻结改变了地表反照率,改变了向上短波辐射,且由于冻结过程减缓了地表温度的下降,改变了地表向上长波辐射,进而改变了净辐射通量;(3)冻融过程显著地改变了陆面能量的分配,通过相变能量的释放和吸收增大了地气间能量的传输,显著地增大了地表土壤热通量,且通过改变地表温度和地表蒸发,改变了感热及潜热通量。在冻结过程及完全冻结阶段,感热及潜热通量均增大,但在消融过程阶段,感热及潜热通量均减小。冻融过程对土壤热通量及感热通量的影响在冻结过程及完全冻结阶段更为显著,而对潜热的影响则是在消融过程阶段更为显著。

Using observational data from Zoige Station in the east of the Tibetan Plateau and the land surface process model, Community Land Model version 3.5 （ CLM3.5 ）, a degradation experiment, in which the freez- ing and thawing process of the model had been removed, was designed, then a simulation experiment for one year was conducted. Through comparison of the results between the original simulation and the sensitive experi- ment, the role of freezing and thawing process in the change of soil temperature and distribution of energy flux was preliminary analyzed. The conclusions are as follows： （ 1 ） Freezing and thawing process is a ＂buffer＂ for the change of soil temperature. Releasing the phase change energy to the environment during freeze slows the cooling rate of soil, which also makes the soil temperature not too low; while absorbing the phase change energy from the environment during the thaw slows the heating rate of soil. （2） Freezing and thawing process changes the surface radiation. The freeze of soil changes surface albedo, which changes the upward shortwave radiation. Due to the buffer role of freezing and thawing process, which delays the decrease of soil surface temperature, the upward longwave radiation is changed actually, which leads to variation of net radiation. （3） Freezing and tha- wing process remarkably changes the distribution of land surface energy. The release and absorption of phase change energy changes the transportation of energy between land and atmosphere, which also changes the sensi- ble heat flux and latent heat flux by changing the surface temperature and surface evaporation. During the freez- ing process and the complete freezing phase, the sensible and latent heat flux increases, but the heat and latent heat flux decreases during the thawing process. The influence of freezing and thawing process on soil heat flux and sensible heat flux is more significant during the freezing process and the complete freezing phase, while that on latent heat flux is more significant during the thawing process.